The Modification of Developmental Patterns in the Sand Dollar by Thiourea

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Abstract
Newly fertilized eggs and 6-hour blastulae of Dendraster excentricus were placed in solutions of thiourea (100 cc. of sea water plus 5-20 cc.of 0.54 M thiourea) for periods ranging from 6 to 60 hrs. The effects at critical concn. and exposure intervals on developmental pattern were similar to those produced by numerous and very different agents (lithium, azide, pilocarpine, thiocyanate, cyanide, tobacco smoke, crowding, etc.). Beginning with the newly fertilized egg continuous exposure to the lower concn. inhibited oral lobes and anal arms and caused approx. 20% exogastrulation. With the higher concn. the ectoderm became more inhibited and the size of the evaginated entoderm increased. Modifications caused by exposure to thiourea beginning at the blastula stage were not greatly different from those caused by exposure of the newly fertilized egg. Blastulae, however, were able to tolerate concns. that were lethal to the uncleaved egg. In the highest concn. entodermal development as well as ventrodor-sality were inhibited although a certain degree of polarity still persisted. Thiourea was less effective in the production of exogastrulae than sodium azide, possibly because azide is a better inhibitor of cytochrome oxidase activity[long dash]an activity that parallels and may be an important correlate of the primary gradient system of this egg.